A power converter is simply a device that converts energy from an input source to produce a regulated output source of energy. Although there are many types and applications for power converters, one such type is a switching, direct current (DC) to DC, step-down power converter, or "buck" regulator, for use in computers and the like.
FIG. 1 illustrates a conventional non-synchronous buck regulator, designated generally by the reference numeral 10. The buck regulator 10 receives an input voltage V.sub.IN and drives an output voltage V.sub.OUT and an output current I.sub.OUT for use by a load Z, such that V.sub.OUT &lt;V.sub.IN. The buck regulator 10 comprises a switch S1, which is typically a field effect transistor ("FET"), a diode D1, an inductor L1 and a capacitor C1. A control circuit 12 turns the switch "off" and "on", i.e., non-conducting and conducting, respectively, as discussed in greater detail below.
The buck regulator 10 operates on the principle of pulse width modulation to provide "point-of-load" voltage regulation. Point-of-load voltage is the voltage level directly at the load Z. A voltage V.sub.D1, across the diode D1 is manipulated in such a way that the output voltage V.sub.OUT maintains the point-of-load voltage at a regulated voltage level.
The control circuit 12 modulates the switch S1 between "off" and "on" for specific periods, or pulses, of time, referred to as pulse width modulation ("PWM"). In this way, the control circuit 12 controls the duty cycle of the switch S1, and thereby controls the output voltage V.sub.OUT. Switching regulators such as the buck regulator 10 have conventionally used dedicated PWM chips for the control circuit 12.
Conventional dedicated PWM chips have only moderate performance responses to sharp changes in the point-of-load voltage at the load Z. When the load Z has a sharp transient response, it increases the output current I.sub.OUT and thereby causes the output voltage V.sub.OUT to sharply fall. As a result, the PWM chip must increase the duty cycle so that it may rapidly pull the output voltage V.sub.OUT back to the desired point-of-load voltage level.
The PWM chip increases the duty cycle by increasing the "on" time and decreasing the "off" time of the switch S1, thereby maintaining a fixed frequency. The changes in the duty cycle occur incrementally, i.e., the PWM chip can not make large and instantaneous changes in the duty cycle. The changes in the duty cycle are also restricted by the fixed frequency because the "on" time can not exceed the frequency period. Because of the small change in pulse width, the point-of-load voltage and output voltage V.sub.OUT will continue to drop until the regulator has sufficiently increased the duty cycle. As a result, hard and/or soft errors may occur in the load Z, depending on the sensitivity of the load to large swings in the point-of-load voltage.
In addition, dedicated PWM chips are relatively expensive. As a result, one solution has been to use linear regulators. Linear regulators are often fairly inexpensive and very simple, by contrast, to the buck regulator 10. However, linear regulators require substantial heat sinking. Typically, for higher power levels, an extruded heat sink is required, even when used with an auxiliary fan. Thus while the regulators are low in cost and easy to manufacture, they have poor thermal performance. As a result, the cost savings from using a linear regulator are expended on thermal management using a heat sink and/or auxiliary fan.
Therefore, what is needed is a power converter such as a buck regulator with a control circuit that is relatively inexpensive.
Furthermore what is needed is a power converter which does not have the thermal penalties of a conventional linear regulator.
Furthermore what is needed is a power converter such as a buck regulator, with relatively sharp responses to transients in the point-of-load voltage.